Method and Apparatus for Planting and Harvesting Radioisotopes on a Mass Production Basis

ABSTRACT

A method and apparatus for modifying an existing nuclear reactor moveable in-core detector system to insert and withdraw target specimens from a reactor core during reactor operation without practically impeding the moveable in-core detector system&#39;s ability to obtain flux maps of the core throughout the reactor&#39;s operation. The apparatus provides a separate drive unit and delivery cable that is independent of the detector drive system, but uses most of the same core delivery conduits to access the core. A specimen holder is remotely detachable from the delivery cable when appropriately positioned and can be remotely reattached for withdrawal after a scheduled period of radiation.

BACKGROUND 1. Field

This invention pertains generally to methods and devices for theinsertion and removal of radioactive isotopes into and out of a nuclearcore and, more particularly, to the insertion and removal of suchisotopes into and out of a commercial nuclear reactor on a massproduction basis without reducing the reactor's facilities ability togenerate electricity.

2. Related Art

The commercial production of radioactive isotopes for medical and othercommercial enterprises, such as Radioisotope Thermal Generators (RTG),is a process which is limited by the very high costs associated withdeveloping the neutron source infrastructure required to createcommercial quantities of the useful isotopes. This makes the usefulapplications of these radioactive isotopes very expensive and subject toextreme supply and cost fluctuations due to actual or perceivedpotential interruptions at the very limited number of isotope productionfacilities available. The human cost associated with this situation isthat most people are not able to afford the cost of the medical benefitsthat can be provided by the large number of available radioactiveisotope diagnostic and treatment modalities.

Furthermore, the reactors that are currently used to produce theradioisotopes that are processed to produce radio-pharmaceuticals arevery old, and continued operation requires very expensive upgrades thatappear to provide poor return on investment. Consequently, the reactorresources required to maintain existing production capability isdisappearing. The fundamental issue to be addressed is the loss ofmedical radioisotope production capability due to obsolescence issues inthe existing medical radioisotope production infrastructure that willlead to a shortage of the radioisotopes needed to diagnose and treatserious medical issues. Accordingly, a need exists for an alternative,and preferably less expensive, way of producing radioisotopes.

A number of operating nuclear reactors used in commercial electricalgeneration facilities employ a moveable in-core detector system such asthe one described in U.S. Pat. No. 3,932,211, to periodically measurethe axial and radial power distribution within the core. The moveabledetector system generally comprises four, five or six detector/driveassemblies, depending upon the size of the plant (two, three or fourloops), which are interconnected in such a fashion that they can assessvarious combinations of in-core flux thimbles. To obtain the thimbleinterconnection capability, each detector has associated with it a fiveor six-path and ten or fifteen-path rotary mechanical transfer device. Acore map is made by selecting, by way of the transfer devices,particular thimbles through which the detectors are driven. To minimizemapping time, each detector is capable of being run at high speed (72feet per minute) from its withdrawn position to a point just below thecore. At this point, the detector speed is reduced to 12 feet per minuteand the detector traversed to the top of the core, direction reversed,and the detector traversed to the bottom of the core. The detector speedis then increased to 72 feet per minute and the detector is moved to itswithdrawn position. A new flux thimble is selected for mapping byrotating the transfer devices and the above procedure repeated.

FIG. 1 shows the basic system for the insertion of the movable miniaturedetectors. Retractable thimbles 10, into which the miniature detectors12 are driven, take the routes approximately as shown. The thimbles areinserted into the reactor core 14 through conduits extending from thebottom of the reactor vessel 16 through the concrete shield area 18 andthen up to a thimble seal table 20. Since the movable detector thimblesare closed at the leading (reactor) end, they are dry inside. Thethimbles, thus, serve as a pressure barrier between the reactor waterpressure (2500 psig design) and the atmosphere. Mechanical seals betweenthe retractable thimbles and the conduits are provided at the seal table20. The conduits 22 are essentially extensions of the reactor vessel 16,with the thimbles allowing the insertion of the in-core instrumentationmovable miniature detectors. During operation, the thimbles 10 arestationary and will be retracted only under depressurized conditionsduring refueling or maintenance operations. Withdrawal of a thimble tothe bottom of the reactor vessel is also possible if work is required onthe vessel internals.

The drive system for insertion of the miniature detectors includes,basically, drive units 24, limit switch assemblies 26, five-path rotarytransfer devices 28, 10-path rotary transfer devices 30, and isolationvalves 32, as shown. Each drive unit pushes a hollow helical wrap drivecable into the core with a miniature detector attached to the leadingend of the cable and a small diameter coaxial cable, which communicatesthe detector output, threaded through the hollow center back to thetrailing end of the drive cable.

The use of the moveable in-core detector system flux thimbles 10 for theproduction of irradiation desired neutron activation and transmutationproducts, such as isotopes used in medical procedures, requires a meansto insert and withdraw the material to be irradiated from inside theflux thimbles located in the reactor core 14. Preferably, the means usedminimizes the potential for radiation exposure to personnel during theproduction process and also minimizes the amount of radioactive wastegenerated during this process. In order to precisely monitor the neutronexposure received by the target material to ensure the amount ofactivation or transmutation product being produced is adequate, it isnecessary for the device to allow an indication of neutron flux in thevicinity of the target material to be continuously measured. Ideally,the means used would be compatible with systems currently used to insertand withdraw sensors within the core of commercial nuclear reactors.Co-pending U.S. patent application Ser. No. 15/210,231, entitledIrradiation Target Handling Device, filed Jul. 14, 2016, describes anIsotope Production Cable Assembly that satisfies all the importantconsiderations described above for the production of medical isotopesthat need core exposure for less than a full fuel cycle.

There are other commercially valuable radioisotopes that are producedvia neutron transmutation that require multiple neuron inducedtransmutation reactions to occur in order to produce the desiredradioisotope product, or are derived from materials having a very lowneutron interaction cross section, such as Co-60, W-188, Ni-63, Bi-213and Ac-225. These isotopes require a core residence time of a fuel cycleor more. Commercial power reactors have an abundance of neutrons that donot significantly contribute to the heat output from the reactor used togenerate electrical power. This invention describes a process andassociated hardware that may be used to utilize the neutron environmentin a commercial nuclear reactor to produce commercially valuablequantities of radioisotopes that require long-term neutron exposure,i.e., a fuel cycle or longer, or short term exposure, i.e., less thanone fuel cycle, with minimal impact on reactor operations and operatingcosts. The hardware and methodology described in U.S. patent applicationSer. No. 15/341,478, filed Nov. 2, 2016, will enable the production ofradioisotopes that require relatively long residence times in the core,currently produced in outdated isotope production reactors, using theforegoing moveable in-core detector system equipment without interferingwith the functionality of the moveable in-core detector system powerdistribution measurement process.

There is still a further need for a more efficient radioisotopeproduction process that can produce radioisotopes in commercial nuclearreactors on a mass production scale, without negatively impacting theelectrical power output of those commercial facilities. It is an objectof this invention to satisfy that need.

SUMMARY

This and other objects are achieved, in accordance with this invention,with an irradiation target handling system having an isotope productioncable assembly comprising a target holder drive cable constructed to becompatible with conduits of an existing nuclear reactor moveable in-coredetector system that convey in-core detectors from a detector drivesystem to and through instrument thimbles within a reactor core. Thetarget holder drive cable has a remotely controlled one of a male orfemale coupling on a leading end of the drive cable. A target holderdrive cable drive motor unit is provided separate from and independentof the detector drive unit on the existing nuclear reactor moveablein-core detector system. The target holder drive cable drive motor unitis configured to drive the target holder drive cable into and out of thecore and is structured to drive the target holder drive cable into andthrough the conduits, a first multipath selector and a second multipathselector on the existing nuclear reactor moveable in-core detectorsystem. A specimen target holder is provided having another of the maleor female coupling on a trailing end of the specimen target holder withthe another of the male or female coupling configured to mate with theone of the male or female coupling on the leading end of the targetholder drive cable. A third multipath selector is connected to andstructured to receive an input from an outlet path on the secondmultipath selector and provides a first output to a new specimenattachment location, a second output to an irradiated specimenoffloading location and a third output to the core.

In one embodiment the specimen target holder has a radial projectionextending from or through an outside wall of the specimen target holderinto contact with an interior wall of an instrument thimble in thereactor core, into which the specimen target holder is driven by thetarget holder drive cable, which maintains an axial position of thespecimen holder within the instrument thimble, when the specimen holderis detached from the drive cable. Preferably, the one of the male orfemale coupling is configured to move the radial projection away fromthe interior wall of the instrument thimble when coupled to another ofthe male or female coupling on the specimen target holder.

In still another embodiment the irradiation target handling systemincludes an axial positioning device attached to the specimen targetholder for determining when the specimen target holder achieves apreselected axial position within an instrument thimble within the core,which the specimen target holder is driven into by the drive cable.Preferably, the instrument thimbles have a closed upper end and aleading end of the specimen target holder has an axial projection thatis sized to contact an interior of the closed upper end of theinstrument thimble into which the specimen target holder is driven. Inone such embodiment the length of the axial projection is a wire havingan adjustable length. Desirably, the target holder drive cable entersthe conduits through a “Y” connection with one leg of the “Y” connectedto the target holder drive cable drive motor unit and a second leg ofthe “Y” connected to the detector drive unit.

The invention also contemplates a method of irradiating multiplespecimens within a core of a nuclear reactor that has a moveablein-core, radiation detector flux mapping system, wherein the corecomprises a plurality of fuel assemblies respectively having instrumentthimbles into which a radiation detector of the flux mapping system canbe inserted and travel through. The method comprises the step ofinserting a first specimen holder containing a first specimen at a leadend of a first drive cable driven by a first drive unit, into a firstinstrument thimble in the core. Next, the method remotely detaches thefirst drive cable from the first specimen holder and fixes an axialposition of the first specimen holder within the first instrumentthimble. Then the first drive cable is withdrawn from the reactor. Next,a second specimen holder containing a second specimen is attached to thelead end of the first drive cable driven by the first drive unit. Thesecond specimen holder containing the second specimen is then insertedinto a second instrument thimble in the core. The first drive cable isnext remotely detached from the second specimen holder and the secondspecimen holder is fixed at an axial position that it was driven towithin the second instrument thimble. The next step withdraws the firstdrive cable from the reactor. In between the withdrawing step and thesecond inserting step, the method inserts a moveable in-core radiationdetector from the moveable in-core detector radiation flux mappingsystem, attached to a second drive cable driven by a second drive unit,into and through a third instrument thimble and withdraws the moveablein-core radiation detector from the reactor after performing a fluxmapping exercise.

In one embodiment of the method, the inserting steps insert specimenholders into as many as half the instrument thimbles accessible by theflux mapping system for simultaneous irradiation at a time when a fluxmap is to be conducted. Preferably, the steps of fixing the axialposition of the specimen holders within the respective instrumentthimbles includes the steps of determining when the respective specimenholders are at a preselected axial position within the correspondinginstrument thimbles. In one such embodiment, the step of withdrawing thefirst drive cable from the reactor comprises withdrawing the first drivecable out of the moveable in-core, radiation detector flux mappingsystem prior to the running of a flux map.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the invention can be gained from thefollowing description of the preferred embodiments when read inconjunction with the accompanying drawings in which:

FIG. 1 is a schematic, elevational view, partially in section,illustrating the basic flux mapping system that can be employed inaccordance with this invention to produce a plurality of targetisotopes;

FIG. 2 is a schematic view of a modification to the flux mapping systemshown in FIG. 1 to configure the apparatus to perform the method of thisinvention;

FIG. 3 is a schematic cutaway view of one embodiment of the targetholder drive cable assembly of this invention;

FIG. 3A is an enlarged view of the latch plug shown on the lead end ofthe specimen holder drive cable shown in FIG. 3; and

FIG. 3B is an end view of the trailing end of the specimen holder shownin FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT

To accomplish the foregoing objectives, this invention modifies thetraditional flux mapping system described above with respect to FIG. 1,as shown in FIG. 2. FIG. 2 shows a portion of the moveable in-coredetector flux mapping system containing the detector drive unit 24, thefive-path transfer device 28, the ten-path transfer device 30 and theseal table 20 in schematic form with the incidental components, like thelimit switches, safety switches and isolation valves omitted. Also shownin FIG. 2 are the core components of the modifications introduced bythis invention to the moveable in-core detector flux mapping system, toconvert the moveable in-core detector flux mapping system into aradioisotope mass production facility, without compromising the fluxmapping function. In accordance with this invention a specimen holdercable drive unit 34 is provided that is distinct and independent of thedetector drive unit 24. The specimen holder cable drive unit 34 drives aspecimen holder drive cable 36 that has a specimen holder 48 detachablyattached to the lead end of the specimen holder drive cable 36. Thespecimen holder 48 is shown in and will be described in more detail withregard to FIG. 3. It should also be appreciated that the specimen holdercable drive unit 34 and the specimen holder cable 36 may be configuredthe same as the detector motor drive unit 24 and the detector drivecable 50, though other configurations are also compatible with thisinvention. The specimen holder drive cable 36 is fed into the conduitsof the moveable detector in-core flux mapping system through a “Y”connection 38 that communicates with the input to the five-path transferdevice 28. One of the outputs of the five-path transfer device similarlyfeeds the input to the ten-path transfer device 30, one of the outputs52 of which feeds a new three-path transfer device 40. One output of thethree-path transfer device feeds a new specimen attachment point 42, atwhich a new specimen holder and specimen can be attached to the specimenholder drive cable; a second output of the three-path transfer devicefeeds a specimen holder catcher in which the specimen holder can beoffloaded; and a third output of the three-path transfer device providesa path to the core. It should be appreciated that while five-path,ten-path and three-path transfer devices are disclosed these devices mayhave as many paths as necessary to access the desired locations withinthe core and currently five-path and six-path devices 28 and ten-pathand fifteen-path devices 30 are in use or planned for use, depending onthe size of the core.

FIG. 3 shows the lead end of the specimen holder drive cable 36 and thespecimen holder 48. The specimen holder drive cable 36 has a spiral wirewrap 56 that mates with drive gears in the specimen holder drive motorunit 34 to advance and withdraw the specimen holder drive cable 36through the conduits of the flux mapping system. At the lead end of thespecimen holder drive cable 36 is a remotely operated male couplingcomponent 58 that fits within a female coupling component 60 on thespecimen holder 48. The male coupling component 58 has a remotelyoperated pneumatic latch plug 62 that when fully activated in itsextended position fits within an annular groove 64 in the femalecoupling component 60. The latch plug 62 is shown in more detail in FIG.3A, in the activated position, and includes an unlatching spring 66 thatretracts the latch plug 62 when the pneumatic pressure supplied throughthe pneumatic fluid supply channel 70 is released. The pneumatic fluidis supplied from a pneumatic fluid supply reservoir 46, shown in FIG. 2,through the pneumatic fluid supply channel 70 that runs through thecenter of the specimen holder drive cable 36. A retaining clip 68prevents the latch plug 62 from leaving the channel in which it travels.The specimen holder 48 has a payload chamber 72 that houses the specimento be irradiated and two or more positioning tabs 76 that extend from aninterior of the specimen holder housing 74, through the specimen holderhousing and up against an interior surface of a fuel assembly instrumentthimble in which the specimen holder 48 is to be inserted, to hold thespecimen holder in position, by friction, when it is remotelydisconnected from the specimen holder drive cable 36. The positioningtabs 76 are biased in a fully extended position and are rotated out ofcontact with the side walls of the instrument thimble by the malecoupling component 58 when the male coupling component is fully insertedinto the female coupling component 60. An end view of the positioningtabs 76 is shown in FIG. 3B. The specimen holder 48 also has anadjustable positioning cable 78 which extends out the lead end of thespecimen holder 48. The desired axial position of the specimen withinthe instrument thimble is determined in advance of inserting thespecimen into the moveable in-core detector flux mapping system and thelength of the positioning cable 78 is adjusted so its lead end abuts theclosed upper end of the instrument thimble when the specimen is at thedesired position.

Thus, in between flux map runs, which are typically conducted once aquarter, the moveable in-core detector flux mapping system is availableto insert isotopes into and harvest isotopes from all of the instrumentthimbles in a reactor core accessible to the flux mapping system, solong as at least fifty percent of those thimbles are unoccupied at thetime a flux map is to be run. Prior to a flux mapping run, the specimenholder drive cable 36 has to be withdrawn above the “Y’ connection 38 toprovide the miniature detector access to the five-path transfer device28. Similarly, once a flux mapping run is completed, the miniaturedetector needs to be withdrawn above the “Y” connection to provide thespecimen holder drive cable 36 access to the five-path transfer device28. It should be appreciated that a typical reactor facility employing amoveable in-core flux mapping system has four, five or six parallel,interconnected trains of detectors whose detector drive cables can berun simultaneously so long as they are routed through different conduitsto the core. In accordance with this invention each one of the detectortrains can be provided with its own specimen holder cable drive unitthat are individually programmed to plant isotopes at different desiredlocations within the core.

Thus, this invention provides modifications to an existing moveablein-core detector system and a method to perform the following functionsthat: (i) enables the insertion of specially configured specimensthrough a specially configured access to the existing multi-pathtransfer devices from one or more detector drive trains that enable thespecimen to be inserted into a desired radial reactor core location thatcan be reached through the existing multi-path routing options; (ii)enables the specimen to be inserted into the desired available corelocation at a predetermined axial position inside the moveable in-coredetector system instrument thimble relative to the top of the activefuel in the desired fuel assembly; (iii) enables the specimen holderdrive cable to be disconnected from the specimen holder and withdrawnfrom the reactor above the multipath transfer devices with the axialposition of the specimen in the reactor fixed by mechanical features onthe specimen holder side of the specimen holder drive cable connector;(iv) enables the specimen holder drive cable to be inserted through aspecific existing multi-path transfer device position selection toanother specially configured transfer device, located downstream of theexisting multi-path transfer devices (hereafter referred to as the lowerpath selector), that has a position that enables the specimen holderdrive cable end to reach a location that enables the specimen holderdrive cable to have another specimen holder payload attached; (v)enables a new specimen to be withdrawn above the existing multi-pathtransfer devices and then repeat the above steps 1 through 4 until allthe desired specimens are “planted” in the reactor core as planned; (vi)enables the specimen holder drive cable to be inserted into a plantedspecimen location so that the mating portions of the specimen holderdrive cable connector are brought together to enable the latching plugson the drive cable side of the connector to be activated using apneumatic fluid, such as nitrogen, to pressurize the pneumatic fluidsupply channel so the latch plugs insert into the latch channel locatedon the specimen side of the connector so that the specimen holder can bewithdrawn, or “harvested,” following completion of the desiredirradiation levels; (vii) enables the harvested specimen to be withdrawnthrough the ten-path selector device where the specimen holder latch tothe drive cable is released by reducing the applied pneumatic fluidpressure, and then it is inserted through the lower path selectorposition that enables insertion of the specimen holder until it iscaptured by a device designed to coil the specimen holder with thespecimen payload, to fit within the payload bay of a radioactivematerial transfer cask used for transportation of the specimen to aprocessing facility; (viii) enables the specimen holder cable to bepositioned as described in step 4, above, and repeat steps 1 through 5as desired; and (ix) enables steps 1 through 8 to be repeated asdesired.

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. Accordingly, theparticular embodiments disclosed are meant to be illustrative only andnot limiting as to the scope of the invention which is to be given thefull breadth of the appended claims and any and all equivalents thereof.

What is claimed is:
 1. An irradiation target handling system having anisotope production cable assembly comprising: a target holder drivecable constructed to be compatible with conduits of an existing nuclearreactor moveable in-core detector system that convey in-core detectorsfrom a detector drive unit to and through instrument thimbles within areactor core, the target holder drive cable having a remotely controlledone of a male or female coupling on a leading end of the drive cable; atarget holder drive cable drive motor unit separate from and independentof the detector drive unit on the existing nuclear reactor moveablein-core detector system and configured to drive the target holder drivecable into and out of the core, wherein the target holder drive cabledrive motor unit is structured to drive the target holder drive cableinto and through the conduits, a first multipath selector and a secondmultipath selector on the existing nuclear reactor moveable in-coredetector system; a specimen target holder having another of the male orfemale coupling on a trailing end of the specimen target holder with theanother of the male or female coupling configured to mate with the oneof the male or female coupling on the leading end of the target holderdrive cable; and a third multipath selector structured to receive aninput from an outlet path on the second multipath selector and provide afirst output to a new specimen attachment location, a second output toan irradiated specimen offloading location and a third output to thecore.
 2. The irradiation target handling system of claim 1 wherein thespecimen target holder has a radial projection extending from or throughan outside wall of the specimen target holder into contact with aninterior wall of an instrument thimble in the reactor core, into whichthe specimen target holder is driven by the target holder drive cable,which maintains an axial position of the specimen holder within theinstrument thimble, when the specimen holder is detached from the drivecable.
 3. The irradiation target handling system of claim 2 wherein theone of the male or female coupling is configured to move the radialprojection away from the interior wall of the instrument thimble whencoupled to the another of the male or female coupling on the specimentarget holder.
 4. The irradiation target handling system of claim 1including an axial positioning device attached to the specimen targetholder for determining when the specimen target holder achieves apreselected axial position within an instrument thimble within the core,which the specimen target holder is driven into by the drive cable. 5.The irradiation target handling system of claim 4 wherein the instrumentthimbles have a closed upper end and a leading end of the specimentarget holder has an axial projection that is sized to contact aninterior of the closed upper end of the instrument thimble into whichthe specimen target holder is driven.
 6. The irradiation target handlingsystem of claim 5 wherein the length of the axial projection is a wirehaving an adjustable length.
 7. The irradiation target handling systemof claim 1 wherein the target holder drive cable enters the conduitsthrough a “Y” connection with one leg of the “Y” connected to the targetholder drive cable drive motor unit and a second leg of the “Y”connected to the detector drive unit.
 8. A method of irradiatingmultiple specimens within a core of a nuclear reactor that has amoveable in-core, radiation detector flux mapping system, wherein thecore comprises a plurality of fuel assemblies respectively havinginstrument thimbles into which a radiation detector of the flux mappingsystem can be inserted and travel through, comprising the steps of:inserting a first specimen holder containing a first specimen at a leadend of a first drive cable driven by a first drive unit, into a firstinstrument thimble in the core; remotely detaching the first drive cablefrom the first specimen holder and fixing an axial position of the firstspecimen holder within the first instrument thimble; withdrawing thefirst drive cable from the reactor; attaching a second specimen holdercontaining a second specimen to the lead end of the first drive cabledriven by the first drive unit; inserting the second specimen holdercontaining the second specimen into a second instrument thimble in thecore; remotely detaching the first drive cable from the second specimenholder and fixing an axial position of the second specimen holder withinthe second instrument thimble; withdrawing the first drive cable fromthe reactor; in between the withdrawing step and the second insertingstep inserting a moveable in-core radiation detector from the moveablein-core detector radiation flux mapping system, attached to a seconddrive cable driven by a second drive unit, into and through a thirdinstrument thimble; and withdrawing the moveable in-core radiationdetector from the reactor after performing a flux mapping exercise. 9.The method of claim 8 wherein the inserting steps insert specimenholders into as many as half the instrument thimbles accessible by theflux mapping system for simultaneous irradiation at a time when a fluxmap is to be conducted.
 10. The method of claim 8 wherein the steps offixing the axial position of the specimen holders within the respectiveinstrument thimbles includes the steps of determining when therespective specimen holders are at a preselected axial position withinthe corresponding instrument thimbles.
 11. The method of claim 8 whereinthe step of withdrawing the first drive cable from the reactor compriseswithdrawing the first drive cable out of the moveable in-core, radiationdetector flux mapping system prior to the running of a flux map.